1. Field of the Invention
The present invention relates generally to drawing and ironing (D&I) presses such as those used in forming drawn and ironed containers, and more particularly to an improved lubricating ring for use in such presses.
2. Description of the Related Art
In the formation of a container, it has been customary to utilize dies that cooperate with a punch for converting, for example, circular metal or metalloplastic discs, commonly referred to as blanks, into finished cans or other forms of containers. Typically, this is accomplished in a two-step process. The circular disc is first formed into a cup and then the cup is drawn and ironed through dies to thin and lengthen the side walls. The step of forming the disc into a cup is typically performed in a cupping press while the conversion of the cup into the finished product is performed by a D&I press or bodymaker. In a typical application, the cup may be forced through multiple ironing dies. The bodymaker uses a punch to force the cup through the ironing dies to form the finished container.
In ironing the side wall of the cup to create the finished container, the workpiece is severely worked as it passes through the dies. Typically, bodymakers operate at very high speeds to efficiently produce the required volume of finished containers economically. For example, a single bodymaker may be operated to produce 300 to 500 or more finished containers per minute. Such high speed operation adds to the stress on the dies and to the heat generated during the process.
To minimize the amount of friction between the workpiece and die components, and the associated heat generated therein, it is customary to lubricate the surfaces of the dies which actually contact the workpiece, i.e., the die nibs. The nib may be formed of carbide or other material of suitable strength for the intended application. The lubricant reduces friction between the nib and workpiece during container formation and also serves as a coolant.
Without proper lubrication and cooling, the workpiece may be distorted or torn, and the die nibs may be damaged or their life reduced, during working of the container. Additionally, increased metal fines or shavings from the workpiece may be produced, thus reducing the life and/or effectiveness of the lubricant itself and lubricant filter. Further, if cooling is insufficient, the distance between the opposed surfaces of the nib and punch may increase or decrease, depending on the nib and punch materials, to an undesirable level making it impossible to produce containers having the required sidewall thickness. For example, if a carbide die nib and steel punch are utilized, the punch will have a greater coefficient of expansion than the nib. Accordingly, as the heat generated during the working of a workpiece increases, the distance between the punch and die nib will decrease to an unacceptable level. On the other hand, if both the punch and nib are formed of carbide, the punch will typically stay somewhat cooler than the nib. As the heat generated during the working of the workpiece increases, the distance between the punch and nib may actually increase to an unacceptable level. In a typical can making application, if the distance between the nib and punch diameters are out of tolerance by more than 0.0002 inches, e.g. more than 0.0001 inches on each side, the finished container will either have sidewalls which are formed too thin or too thick. If the sidewalls are too thin the container will generally fail to meet the customer's specification. If too thick, the resulting finished container may have sidewalls of insufficient length to provide enough excess material to allow the end of the finished container to be cut to form a smooth edge surface.
Numerous techniques for lubricating and cooling the dies and the workpiece have been proposed. Such techniques have generally provided for a continuous flow of the lubricating fluid during operation of the bodymaker so that cooling can continue even when no workpiece is being worked by the press.
Lubricating rings formed as part of a die assembly with drop-in dies, or formed separate from but arranged adjacent to the dies in a tool pack assembly, are often utilized to direct lubricant into the die cavity through which the workpiece will be drawn and ironed into the finished container. The lube rings function to orient and direct the flow of the lubricant toward the die nibs. More particularly, holes, channels or grooves are machined into the lube ring to direct pressurized lubricating fluid toward the portion of the die nibs which will come in contact with the workpiece to thin and lengthen the side walls of the cup and thereby form the desired finished container. The lubricant may, for example, be composed of water in combination with oils, fats or other materials having suitable qualities.
In practice, the orienting and directing of the flow of lubricant is not a simple task because the working surface of the nib is on the inner periphery of the tool pack or die assembly cavity through which the workpiece is drawn by the punch. The inner diameter of the lube ring must be greater than the diameter of the working surfaces of the nibs so as to avoid interference with the workpiece as it passes through the cavity. Hence, it is extremely difficult to direct a fluid spray onto the working surface of the nib.
Lube rings have been proposed with a circular array of small holes which are angled to direct a fluid spray as close as possible to the working surface of the nibs. Other proposed lube rings have a groove machined into the ring which is formed so that the lubricant is squeezed out of the groove at an angle so as to direct a lubricant spray as close as practicable to the working surface of each nib. Still other proposed lube rings include a circular array of slots machined into the ring to direct a fluid spray toward the working surface of the nibs. In each case, the fluid spray is directed at a high velocity toward the main cavity of the press die assembly or tool pack and the working surface of the nibs. Such lube rings, at best, provide less than optimum lubrication to the nib working surface. This is because proposed lube rings fail to deliver the lubricant so that the die nibs are completely and uniformly coated. Further, a slightly improper orientation of the ring outlet(s) or a minor change in the velocity of the fluid from the outlet(s) can result in the lubricant jetting past or otherwise missing the working surface of the nibs. Hence, sufficient lubrication and cooling will not be provided.
The key to preventing undesirable stresses and heat on the die components and workpiece is to uniformly, completely and consistently coat the working surface of each nib of the ironing die with the desired lubricant. Hence, there is a need for an improved lubricating and cooling technique for use in drawing and ironing workpieces.